Diesel engines require reduction of particulate matter (PM) and nitrogen oxide (NOx) emissions. Future original equipment (OE) for diesel engines will include both NOx catalysts (DeNOx catalysts) and PM after-treatment systems to meet low NOx and PM limits. Because multiple components are needed, however, exhaust systems become more complex and space consuming.
One approach to meet the need for combined PM and NOx control has been to integrate a DeNOx catalyst within a diesel particulate filter (DPF) to reduce volume and decrease backpressure penalty. In this approach, the catalyst and DPF are integrated by loading the catalyst within the DPF wall porosity. However, this type of catalyst addition adversely affects soot-loaded backpressure, even for very high porosity filters (≧65% porosity), which, in addition, are challenging to produce. Such backpressure imposes a severe fuel consumption penalty and complicates regeneration of the DPF.